The invention relates to a process and a plant for shaping ceramic tiles and the like. The invention is usefully employed in the field of decorated vitrified stoneware tile production and the like.
In particular the invention relates to a process for forming ceramic tiles and the like, comprising a first phase in which a layer of powdery material is deposited on a mobile transport plane, in such a way that the powdery material exhibits a pattern. In a second phase the layer of powdery material is transferred internally of a forming cavity of a mould by effect of a movement of the transport plane which causes the powdery material to fall from an edge of the transport plane and by effect of a contemporaneous displacement of the transport plane with respect to the cavity, so that the powdery material is caused to fall internally of the cavity and is deposited in the form of a layer and still exhibiting the pattern. In a third phase the powdery material deposited in the cavity is pressed.
A similar process is known from EP 0 492 733 or EP 0 300 532, wherein a pattern layer of ceramic material is deposited by moving a rotating belt over the forming cavity, on which belt the material of the pattern layer is present. In EP 0 492 733 striated colour patterns are formed in the upper surface of the tiles by means of a conveyor belt whose side receiving the powdery material is provided with grooves disposed in a desired arrangement, into which the material is introduced in order to be subsequently deposited from the grooves into the forming cavity of the mould.
The prior art comprises also EP 0 558 248, which discloses a method for producing ceramic patterned shaped articles, wherein dry particles for a pattern course are lodged in a plurality of spaces provided on an endless pattern-forming device. The supplied particles are temporarily retained in the spaces. Then the particles are released onto a given surface.
A main aim of the invention is to provide a process for forming ceramic tiles which economically and simply enables decorations to be made on tiles which are completely contained within the breadth of the tile itself.
An advantage of the invention is that it enables complex but well-defined multicoloured patterns to be made.
A further advantage is that decorations are obtained on the tiles which reproduce the exterior aspect of stone slabs.
A further aim of the invention is to provide a plant for realising the above process.
These aims and advantages and more besides are achieved by the invention, as it is characterised in the appended claims.
The process of the invention comprises a first phase, wherein a layer of powdery material is deposited on a running conveyor surface. The layer of powdery material is multicoloured so as to give the layer a predetermined pattern or decoration. This is followed by a second phase wherein the deposited powder is transferred into a shaping cavity of a mould, by effect of a movement of the conveyor, which tips the powder from an edge of the conveyor itself; the powder being caused to fall into the cavity, maintaining however the pattern of before. There then follows a third phase in which the powder is pressed in the shaping cavity, before which, if so desired, the powder can be screeded in the cavity. The layer of powdery material formed on the conveyor surface and bearing the decoration is preferably screeded, using means of known type, even before being transferred into the shaping cavity.
In a preferred embodiment of the invention, the first abovementioned phase, in which a decoration in the powder itself is achieved, is preceded by a number of operations in sequence, as follows: filling one or more shaped cavities distributed on a surface according to a predetermined design or decoration; compacting the powder material internally of said cavities; transferring the compacted material on to the moving conveyor, so that the surface of the conveyor is covered with a decorated layer of compacted material, on which more powder material is deposited, not compacted, and either of one colour or several, which second layer covers the decorative compacted material all of which is then deposited in the shaping cavity. The non-compacted material can be deposited on the conveyor before the compacted layer, if so desired, the whole then being deposited in the forming cavity.
The distribution of the powder on the conveyor can be done so that the more aesthetically appealing face, i.e. the one bearing the decoration, is the lower face, but the opposite can also be achieved. The tile can be achieved with the more attractive surface facing either downwards or upwards.
In the above-described process the decoration is included in the powder material before pressing and can be realised, at least partially, using pre-compacted material, which determines very special decorative results in the finished tile, reproducing the natural look of stone materials, such as marble, for example.
In another embodiment of the above-described process, a fraction of the compacted material forming the decoration arranged on the conveyor surface can be broken. Said fraction of the material, due to the, effect of the breaking, is detached from the part of the material which remains compacted and is arranged haphazardly at the edge of the compacted material. This technique gives the finished tiles an ornamental effect which is very similar to the irregularities normally found in stone materials.
The material used for making the tiles is preferably constituted by a mixture or granules or powders, which, after firing, results in a product having the characteristics of vitrified stoneware.
If so desired, a part of the tile breadth can be made using less aesthetically attractive powder; obviously the lower part, including the bottom surface, would normally be the one made with this less attractive material.
After firing, the more attractive of the two faces can be further processed by sanding and buffing.
The invention provides a decoration contained within the tile itself, as it exits from the mould and without any need to add material on the surface of the tile. Very detailed and well-defined patterns and colours can be obtained on vitrified stoneware tiles using the above-described process, without especially complicating the production cycle. The process also offers the possibility of obtaining patterns which very greatly imitate the natural appearance of marble and granites. The invention also enables production of tiles having the type of decoration known as xe2x80x9ctexturedxe2x80x9d, i.e. with parts of the surface in relief, which can then be sanded away or left, as so desired.